Iron nitride magnets offer a low cost alternative to rare earth magnets. In addition, the questionable stability of rare earth magnets on the nanoscale is avoided in the binary iron phases.
It has been shown that the low nitrogen content phases such as γ-Fe4N, ε-Fe2-3N, α′-Fe8N and α″-Fe16N2 are ferromagnetic compounds having exceptionally well characterized stoichiometry and electronic properties and are attractive compounds for magnetic functional nanomaterials. The synthetic routes for commercial production are also well-documented.
Ferromagnetic materials exhibit parallel alignment of moments resulting in large net magnetization even in the absence of a magnetic field. In particular, α″-Fe16N2 phase is the most important compound and can be a possible candidate for high-density magnetic recording media owing to its very high magnetic moment, which is even larger than that of the pure α-Fe. The saturation magnetization and the coercivity of these ferromagnetic phases for iron thin films have been studied by many researchers, since the saturation magnetization is an intrinsic property of materials. Except for the phases of a-Fe8N and α″-Fe16N2, the saturation magnetization of the other ferromagnetic phases is generally lower than that of the a-Fe, which has been proven by most above-mentioned researchers.
These iron nitride nanoparticles can find applications in magnetic memory devices, medical hyperthermia, magnetic drug carriers, and the like. For example, colloidal suspensions of magnetic nanoparticles (MNPs) called ferrofluids have been proposed for a range of biomedical applications such as magnetic gradient-guided drug carriers for targeted drug delivery, cancer thermotherapy, and MRI contrast agents. In thermotherapy, the response of MNPs to AC magnetic field causes thermal energy to be dissipated into the surroundings, killing the tumor cells. Additionally, hyperthermia enhances radiation and chemotherapy treatment of cancer.
Magnetic hyperthermia results from domain switching upon AC EM radiation application. Our previous work investigated iron oxide nanoparticles for heating applications, however, the major mechanism involved in the temperature increases in this particular nanomaterial has, only now, been uncovered. Such applications require a material with a large magnetic moment as well as control of the magnetic properties imparted by superparamagnetism. Therefore, iron-containing nanomaterials with high saturation magnetic moments are attractive. The iron oxides, specifically, have demonstrated high biocompatibility and low systemic toxicity. Others have reported the efficacy of tumor therapy using similar particles and found that the side effects of this therapeutic approach were moderate, and no serious complications were observed. Iron oxide nanoparticles have received FDA approval for use in humans as contrast agents in magnetic resonance imaging (MRI). Superparamagnetic iron oxide nanoparticles (SPIONs) hold potential as drug carriers, since they may be guided (and potentially removed when no longer needed) by the magnetic field toward a specific area of interest, thereby reducing the present effective dose and eliminating systemic side-effects. It is anticipated that other inorganic magnetic materials having higher saturation magnetizations may be of interest as drug carriers, however due to the low LD50 of cobalt and the unknown in vivo biocompatibility of the rare earth elements, iron nitride is an alternative.
There is a need for a better method of manufacturing magnetic iron nitride nanoparticles, especially magnetic Fe16N2 nanoparticles.